1. Field of the Invention
The invention relates to fixing elements consisting of plastic with a foot part for insertion into an oblong hole of a carrier plate. The foot part consists of a head corresponding to the edge of the oblong hole and of a shaft adapted to the width of the oblong hole. The fixing element can be locked in the oblong hole after the insertion of the head by a quarter turn under elastic deformation of the shaft. The shaft includes a middle strut connecting the head to the fixing element. The strut has the width of the oblong hole. A shank is formed on each of the two edges of the middle strut at a right angle and in opposite directions in such a manner that they are elastically bent towards the middle strut during the screwing in of the shaft through the edge of the oblong hole and after a quarter turn they return to their original position as a consequence of the elastic return force of the plastic and thus prevent a rotation in the opposite direction.
2. Description of Related Art
Such fixing elements are known from U.S. Pat. No. 4,981,405. The design of the fixing element with two shanks formed on a shaft at a right angle and in opposite directions opposes a certain resistance to a turning of the fixing elements opposite the direction of screwing. The fixing element advantageously reduces the risk of an unintentional loosening of the fixing element.
Other fixing elements with formed-on shanks are known from U.S. Pat. No. 4,375,879 and U.S. Pat. No. 4,705,442.
DE 1 181 007 describes a fixing element of this type designed as a screw and nut in which the nut shaft that can be inserted into the oblong hole has a width corresponding to the width of the oblong hole and has stop faces running parallel to the screw axis. These stop faces work together with corresponding faces in the oblong hole so that a rotation of the nut is prevented when the screw is tightened. This nut can be readily slackened back again after the screw has been loosened and then can be withdrawn through the oblong hole.
Furthermore, there are fixing elements with a foot part of the above-cited type comparable to the nut and provided with a similarly designed shaft. However, since this foot part is not screwed down, there is the danger that the fixing element can become loose again by an unintended rotary movement.
One advantage of the present fixing element is that it is distinguished by an especially firm seat in the carrier plate.
The present invention is advantageous because it provides for a fixing element with a head having pressing ramps on its two outer ends that extend during screwing in over the edge of the oblong hole and other shanks formed on the free ends of the shanks.
The present invention is also advantageous because it provides for a fixing element having a head with pressing ramps on its two outer ends that extend during screwing in over the edge of the oblong hole and a countershank formed in the opposite direction on each of the two edges of the middle strut.
The providing of the pressing ramps and of the other shanks and countershanks results in an especially firm seat since the fixing element is firmly connected to a carrier plate by the pressing ramps after rotation in the direction of screwing in. Also, an especially great resistance is provided to prevent to an undesired rotation of the fixing elements counter to the direction of screwing in by the other shanks and countershanks.
Other features and advantages of the present invention will be readily appreciated, as the same becomes better understood, after reading the subsequent description taken in conjunction with the accompanying drawings.